The present invention relates to a vehicle seat suspension apparatus, and, more particularly, to an apparatus for controlling and protecting an air suspension system used to support a vehicle seat.
It is well known in the art to use adjustable air suspension systems to provide support for vehicle seats. Typically, these suspensions can be adjusted to accommodate both the weight and height of different seat occupants. An example of such a suspension system is disclosed in U.S. Pat. No. 4,733,847 to Grassl.
Until recently, typical air suspension springs were not completely air tight, and would lose pressure slowly over time. Vehicle seats using these suspensions controlled the air pressure in the spring by a series of sensors and switches. A sensing device was used to determine whether enough air had leaked from the spring to warrant addition of more air. Often a complex assembly of switches and sensors were necessary, employing timing circuits programmed to determine whether the load reduction on the air spring was caused by a brief bounce of the suspension system or a loss of air. Recent developments have enabled the construction of an air spring that, for practical purposes, is air tight and does not require the compensation features of the prior art. Suspensions using these air springs simply control the seat height by an up and down switch that charges or discharges air from the spring. It is desirable, however, to protect these suspension devices so that a vehicle operator does not over-pressurize or under-pressurize the spring, causing inadequate suspension performance or perhaps even permanent damage.
Another problem that has occurred in the use of air suspension devices is the excessive upward movement of the seat when a driver exits the vehicle. If the seat rises too far, it is more difficult for the driver to reenter the vehicle and to readjust the height of the seat, especially in vehicle cabs that are designed with strict height limitations.